Intense-field modulation of NO2 multiphoton dissociation dynamics

Area of Science:

• Physical Chemistry
• Molecular Dynamics
• Laser Spectroscopy

Background:

• Investigating molecular dissociation dynamics under intense laser fields is crucial for understanding light-matter interactions.
• Nitrogen dioxide (NO2) serves as a model system for studying photodissociation processes due to its accessible electronic states.

Purpose of the Study:

• To elucidate the multiphoton excitation and dissociation dynamics of NO2.
• To analyze the influence of laser intensity and wavelength on dissociation pathways and fragment generation.

Main Methods:

• Time-resolved fluorescence spectroscopy was employed to monitor the dissociation of NO2.
• A pump-probe technique was used with varying time delays between the driving and probe laser fields.
• Measurements were conducted at specific wavelengths (395-420 nm) and intensities (4-10 TW cm(-2)).

Main Results:

• Different fluorescence modulation patterns were observed for NO A (2)Sigma(+)n(')=0 and n(')=1 states, indicating distinct dissociation channels.
• The dissociation dynamics were explained by nuclear motion on light-induced potential energy surfaces.
• Intensity-dependent fluorescence decay suggests different mechanisms for generating vibrationally excited vs. ground-state NO fragments.

Conclusions:

• The generation of NO A (2)Sigma(+)n(')=0 is attributed to a light-induced bond-hardening mechanism involving dressed states.
• The prompt decay of NO A (2)Sigma(+)n(')=1 fluorescence points to a direct surface crossing mechanism leading to vibrationally excited products.